T
U B E
C
A R E
& R
E P L A C E M E N T
Like a sports car, there’s a certain amount of wear and tear to be expected in a high-performance tube amp.
Over time, especially with hard use, tubes may need replacement. That’s why it’s a good idea to make note of
when you purchased your amp and whenever you replace tubes. It’s no accident that your amp has two com-
mon types of tubes: They’re great-sounding and reliable, and it’s easy to find replacements. Here’s a tube chart
to show you which tubes go where.
Location
Type
V1
12AX7
V2
12AX7
V3
12AX7
V4
12AX7
V5
12AX7
V6
EL-34
V7
EL-34
V8
EL-34
V9
EL-34
Here’s a brief description of what each tube does:
V1
Input buffer and tone control driver for Channel 2, and also the first preamp stage of Channel 1
V2
Tone control follower for Channel 2 and an additional gain stage for Channel 1
V3
Final stages for both channels before the mixer stage
V4
Reverb follower and the mixer stage, provides gain to the reverb pan
V5
Phase inverter driver tube for the power amp section
V6-V9 Power amp tubes—for best operation, they should always be changed in a group of four
Checking for microphonic tubes
As tubes wear, some problems can come up. One of the most common symptoms is a ringing sound. This is usually
due to the tube becoming microphonic (like its name suggests, it’s picking up sound and amplifying it).
With the amp unplugged and cooled off, examine the tubes to make sure they’re in tight and straight. Never
twist them! Gently grasp the tube and wiggle it into place. Because some of the tubes are inside of metal
sleeves, you will have to remove the sleeves to check them for microphonics. Grasp the sleeve with your fin-
gers and depress it (it’s spring-loaded) and turn to the left (counterclockwise). Now pull it off; this may
require a little wiggling action.
Channel 2
Channel 1
Hundred
Duo Twelve
PULL
SELECT
PULL
BOOST
STANDBY
POWER
LOW
GAIN
HIGH
GAIN
VOLUME
BASS
MIDDLE
TREBLE
MASTER
VOLUME
TREBLE
MIDDLE
BASS
MASTER
REVERB
PRESENCE
HANDCRAFTED BY RIVERA RESEARCH & DEVELOPMENT
SUN VALLEY, CA USA
INPUTS
PULL
BRIGHT
PULL
NOTCH
PULL
NINJA
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
10
9
8
76
5
4
3
2 1
1
18
17
165
V6
V7
V1
V2
V3
V4
V5
V8
V9
